Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.63   8.387%   $261.8955   $261.90   $261.90   $261.90  
  Purchase #2 $148.42   4.129%   $154.5483   $154.55   $154.55   $154.50  
  Purchase #3 $11.41   8.639%   $12.3957   $12.40   $12.40   $12.40  
  Purchase #4 $174.92   3.577%   $181.1769   $181.18   $181.20   $181.20  
  Purchase #5 $248.57   11.490%   $277.1307   $277.13   $277.15   $277.10  
  Purchase #6 $43.70   4.547%   $45.687   $45.69   $45.70   $45.70  
  Purchase #7 $75.36   4.528%   $78.7723   $78.77   $78.75   $78.80  
  7 purchase totals = $944.01       $1,011.6064   $1,011.62   $1,011.65   $1,011.60